android - Firebase 数据库升序分页

Question

我在尝试对来自 firebase 数据库的数据进行分页数周时遇到了一个很好的问题，现在都无济于事。我尝试了从 android 文档到 SO 的所有示例，但仍然无法正常工作。下面是我的数据节点的截图

下面是我的代码，我使用 recycleview 进行连续滚动。

commentDatabaseReference = FirebaseDatabase.getInstance().getReference().child(CHANNEL_COMMENT).child(postId);
commentDatabaseReference.orderByKey().limitToLast(TOTAL_ITEM_EACH_LOAD).addListenerForSingleValueEvent(commentValueEventListener);

ValueEventListener commentValueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(!dataSnapshot.hasChildren()) {
                currentPage--;
            }

            int counter = 0;
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                commentId = snapshot.getKey();
                Comment comment = snapshot.getValue(Comment.class);
                commentList.add(comment);

                adapter.notifyDataSetChanged();
            }
            //adapter.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };

Recycleview 连续滚动监听器

recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener(linearLayoutManager) {

            @Override
            public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
                Log.e("more", "onload");
                loadMoreData();
            }
        }); 

private void loadData() {
        Log.e("loading", ""+ commentId);
        commentDatabaseReference.orderByChild("timestamp").startAt(commentId).limitToLast(TOTAL_ITEM_EACH_LOAD)
                .addListenerForSingleValueEvent(commentValueEventListener);
    }

    private void loadMoreData(){
        //if ((currentPage * TOTAL_ITEM_EACH_LOAD) <= commentCount) {
            currentPage++;
            loadData();
        //}
    }

结论:例如，如果我有 20 个偏移量为 10 的数据，并且我将 orderby 与 limitToLast 一起使用，我会从顶部开始获取最后 10 个数据，即我从 11 - 20 而不是 20 - 11 获取数据。另外注意到当我结合 startAt

时，有时我会得到无穷无尽的数据

Answer 1

最终在 faruk 的提示下解决了这个问题:

下面的代码方法将数据从 firebase 加载到 recycleview

private void loadData() {
        Query query;
        if (commentId == null) {
            query = commentDatabaseReference.orderByChild("timestamp").limitToLast(TOTAL_ITEM_EACH_LOAD);
        } else {
            query = commentDatabaseReference.orderByChild("timestamp").startAt(inverseTimestamp).limitToFirst(TOTAL_ITEM_EACH_LOAD);
        }
        query.addListenerForSingleValueEvent(commentValueEventListener);
    }

    private void loadMoreData(){
        //commentCount: is the total comments stored in firebase database
        if ((currentPage * TOTAL_ITEM_EACH_LOAD) <= commentCount) {
            currentPage++;
            loadData();
        }
    }

在 recycleview 滚动监听器上，我调用了 loadMoreData 方法以从 firebase 获取更多数据

recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener(linearLayoutManager) {

            @Override
            public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
                //Load more data
                loadMoreData();
            }
        });

Firebase 数据库监听器，用于监听获取的数据

ValueEventListener commentValueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(!dataSnapshot.hasChildren()) {
                currentPage--;
            }

            int counter = 0;
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                commentId = snapshot.getKey();//Index key for the node
                Comment comment = snapshot.getValue(Comment.class);

                ++counter;

                //Inverse timestamp
                inverseTimestamp = comment.getTimestamp();

                //store nth - 1 data into the arraylist to avoid duplicates
                if (counter < TOTAL_ITEM_EACH_LOAD) {
                    commentList.add(comment);

                    adapter.notifyDataSetChanged();
                }
            }
            //adapter.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    };